Cardiac resynchronization therapy (CRT) provides an electrical solution to the symptoms and other difficulties brought on by heart failure (HF). CRT can call for delivery of electrical stimuli to the heart in a manner that synchronizes contraction and enhances performance. When CRT delivers stimuli to the right and left ventricles, this is called biventricular pacing. Biventricular pacing aims to improve efficiency of each contraction of the heart and the amount of blood pumped to the body. This helps to lessen the symptoms of heart failure and, in many cases, helps to stop the progression of the disease.
CRT is typically administered via an implantable device such as a pacemaker (e.g., called a CRT-P) or an ICD that has a built-in pacemaker (e.g., called a CRT-D). A CRT-D has the added ability to defibrillate the heart if a patient is at risk for life-threatening arrhythmias. Most traditional ICDs or pacemakers have either one lead placed in the heart's right atrium (RA) or the heart's right ventricle (RV) or two leads where one is placed in the heart's RA and the other is placed in the heart's RV. CRT devices typically have three leads; one placed in the RA, one placed in the RV and one placed in a vein along the left ventricle (LV). Such a configuration allows for bi-ventricular pacing.
Some CRT devices are configured to connect to leads that have series of electrodes that can allow for more optimal delivery of pacing stimuli than leads with few electrodes (e.g., a lead with a tip electrode and a neighboring ring electrode). For example, a CRT platform marketed as the UNITY® platform (St. Jude Medical Corporation, Sylmar, Calif.) is configured for use with a so-called “quartet” LV lead having a quartet of LV electrodes. The UNITY® platform also includes a programmed optimization algorithm marketed as the QUICKOPT® algorithm (St. Jude Medical Corporation, Sylmar, Calif.) that can acquire data and optimize CRT based on the acquired data.
The QUICKOPT® algorithm can perform tests that acquire data and calculate one or more inter-ventricular conduction delays (inter-VCDs) for use in optimizing CRT. A specific inter-VCD is calculated as a difference between a delivery time for a stimulus delivered to one of the ventricles and a sensed activation time of a conducted wavefront responsive to the stimulus in the other ventricle. Such an inter-VCD may be referred to as a paced or stimulated RV-to-LV inter-VCD or a paced or stimulated LV-to-RV inter-VCD where delivery of a stimulus occurs using one ventricular lead (e.g., a LV or RV lead) and where sensing an activation time occurs using another ventricular lead (e.g., a RV or LV lead). Other types of inter-VCDs may be based on intrinsic activity (e.g., an intrinsic RV-to-LV inter-VCD or an intrinsic LV-to-RV inter-VCD). Inter-VCDs can be used for optimizing pacing delays for CRT (e.g., atrial to RV delay (AVRV), atrial to LV delay (AVLV) and/or interventricular delay (VV)).
As described herein, various exemplary techniques allow for optimization of lead and electrode configurations for delivery of cardiac therapies, including CRT, through use of conduction delays, optionally including inter-VCDs.